The code is even more difficult to enter than the past two games' codes, and often needs to be entered two or more times in a row in order for it to take effect. Put the following MAME code in mk3.xml to simplify the code to 2P Block (×3):

Game Audits: Acts like the normal test menu, but with four extra audits on the first page:

Sec Chip Failure

Error Traps

System Lockups

Illegal Opcodes

Volume Adjust: Identical to normal test menu.

Credits: Displays the game credits. Who knew?

Enter Initials: Jumps to the high score initials screen. The number of wins seems to be random, but it increases every time.

Character Endings: Jumps to a new sub-menu. This displays the selected character's ending and the game credits.

Penacho/Miller Game: Jumps to that Galaga-type minigame.

Smoke: Unlocks Smoke.

Un-Smoke: Unlocks Unsmoke. Err, un-unlocks Smoke. Relocks Smoke?

(Source: Original TCRF research)

Unused Sprites

Bell

Using a MAME cheat to break the screen limitations (so you can walk off the edge) reveals an actual BELL in the Bell Tower background. Early gameplay footage shows this and several other bell sprites used in the Bell Tower's foreground and background.

Sheeva's Skeleton

Evidently, Sheeva was supposed to have a unique skeleton sprite for Kano's skeleton rip Fatality.

Ninjas?

Perhaps evidence that the ninjas were planned for inclusion at one point. This was later used for Ermac's Animality in Mortal Kombat Trilogy.

More possible evidence. This was later used for Classic Sub-Zero's friendship in Mortal Kombat Trilogy, as a variant of jack-in-the-box Friendship that Scorpion and Reptile had in Ultimate Mortal Kombat 3.

Motaro

Perhaps evidence that Motaro was meant to be a playable character? This was eventually used for Motaro's win screen when beating the game in Mortal Kombat Trilogy (except the N64 version).

Motaro raising up his front legs. Could have been meant for a victory pose. It also seems to have been meant to be used in combination with the teleportation move.

Motaro doing the teleport. Seems to go with the other front leg raising sprites.

Looks like Motaro was going to throw the opponent over his head. This was used in Mortal Kombat Trilogy as, appropriately, his throw move.

Motaro raising his arm. The mouth moving sprites also go with this, which seems to imply that Motaro was going to have a taunt where he spoke or simply speak at the end of the round.

Nightwolf

Nightwolf swinging an axe with no green glow applied to it.

Unknown Nightwolf sprite, but perhaps it was meant for his holy light Fatality?

Shang Tsung

Sprites meant for a Shang Tsung combo.

Shao Kahn

Shao Kahn swinging his sledgehammer.

A drill meant to be used as either Shao Kahn's Fatality, or merely a special move. A similar sprite is present in Mortal Kombat Trilogy, although that one is shown to be rising out of the ground.

Sindel

Sindel sprite meant for a combo.

Sindel sprites meant for a combo.

Red Herrings

All text is found in chip MK321u.bin, interleaved.

Audits and Transformations

Like Mortal Kombat II, there are a few fake audits. The two in this game are "JOHNNY CAGE TRANSFORMATIONS" (replacing Kano Transformations) and "SHAWN ATTACKS" (left as-is).

A related line can be found at 0x0299BA, after all other match end text, with Johnny's name spelled incorrectly:

JOHHNY CAGE TRANSFORMATION ACTIVATED

Win Text

As in Mortal Kombat II, there's win text in the ROM (starting at 0x02993E) for characters that don't actually appear in the game. This can be further proof that the ninjas were planned for inclusion at one point.